The use of radios in automobiles, recreational vehicles, off-road vehicles, aircraft, boats, ships and buildings is well known. The type of antennas used with these radios and transmitters is determined by several factors; such as, wavelength, size, and weight. The antennas typically used with the receivers, transceivers, and transmitters, are whips, telescoping whips, or other types of electrically short rod antennas that may be electrically loaded or non-loaded. Usually, these antennas make use of the vehicle body as the counterpoise or ground plane part of the antenna system even though some larger vehicles use a loaded vertical dipole arrangement. Even though a dipole antenna does not require a ground plane to complete the antenna system, the ground plane contributes to the overall antenna radiation pattern or gain in the dipole antenna.
For communications with distances that are generally equal to or greater than line-of-sight (LOS), the radios normally operate in the High Frequency (HF) range, which is from about 2 to 30 MHZ. The radios are traditionally used with electrically short whips that are less than a quarter wavelength long with loading coils at the radiator base (base loading) or at the approximate center (center loading), a whip or capacity hat is then provided above the coil to complete the antenna radiating assembly. Even though the center loaded antenna systems are more efficient because of the higher gain than base loaded antennas, the centered loaded antenna systems are mechanically inefficient because of large heavy electrical devices, such as caused when inductors are providing the load, being mounted in the center.
At HF ranges and below, quarter wavelength vertical antennas having no artificial loading are physically too large for standard mobile in motion use. For example, a quarter wavelength antenna operating at 2 MHZ has a length of approximately 117 feet and at 30 MHZ has a length of approximately 8 feet. Even though maritime radios can generally tolerate taller antennas than aeronautical radios, aeronautical antenna designs must meet the aerodynamic requirements of the aircraft with minimum wind drag while maintaining the required radiation efficiency and pattern.
Because of these considerations, a practical mobile antenna is a compromise between a full size vertical antenna with no loading and an antenna with some kind of electrical loading. The design of HF and lower frequency antennas requires serious consideration of maximizing radiation efficiency while at the same time providing a mechanical configuration that has minimum hardware antenna complexity in relation to the vehicle. These considerations apply to all antennas, fixed or mobile stations.
An example of a prior art radio antenna system is described in U.S. Pat. No. 2,313,046. The antenna system described in the patent appears to be used in the 50 to 60 MHZ frequencies (the Very High Frequency band). Thus, the quarter wavelength is many times greater than the length of the antenna structure. The system is adjustable from the base, as opposed to base loading the actual antenna radiator, of the structure to permit a higher degree of efficiency to be readily obtained at selected frequencies within the VHF band of frequencies. It has been discovered that the efficiency of many antenna systems and this prior art system is improved by using the improved electrical transmission line technique disclosed herein.